1. Field of the Invention
Generally, the invention pertains to the field of vacuum thin film position using ion sources. Specifically, the invention focuses upon enhancing the supply of electrons in various regions of the deposition system including the ion source in order to enhance the deposition of thin films onto substrates and expand the range of thin film deposition apparatus, methods, and applications.
2. Brief Description of the Prior Art
The existing literature, such as xe2x80x9cHandbook of Ion sourcesxe2x80x9d edited by Bernard Wolf (CRC Press, 1995), hereby incorporated by reference, teaches that most types of ion sources as well as application apparatus require a source of electrons. In applications of all types of ion sources where the substrate or other surfaces being exposed to ion beam are insulating, the need exists to neutralize the electrical charge induced by the ion beam and this typically is done using an electron source since electrons have negative charge. In addition, those skilled in the field of ion sources know that electron supply plays a fundamental role in the ion source operation. In plasma-type ion sources, the electrons produce ions by ionizing the working gas. The electrons also conduct current such that power can be continuously coupled to the plasma. Therefore, it may be desirable to have electron emitters within the ion source to provide an enhanced continuous supply of electrons.
A significant problem with the use of cold cathode ion sources is that the secondary emission processes that generate electrons in these systems are not very efficient necessitating the use of a high discharge voltage to sustain stable operation. The use of high discharge voltage, however, may lead to defects in the films deposited on the substrate because high discharge voltages may generate fast particles that may subsequently collide with the surface of the substrate.
A significant problem with the use of hot filament thermionic electron emitters is that the operational lifetime of the emitters is very limited, often less than 100 hours. This is especially true when reactive gases, such as oxygen, are present in the ion source. Similarly, a problem with dispenser type thermionic emitters is that the operating life of these units is also limited, and compatibility with reactive gases remains a problem even though such emitters operate at lower temperature and produce higher current as compared to thermionic electron emitters. Similarly, hollow cathode electron emitters have a lifetime of only about 1000 hours as disclosed by U.S. Pat. Nos. 3,156,090; 3,913,320; 3,952,228; 3,956,666; and 3,969,646, each hereby incorporated by reference.
Another problem with existing sputtering techniques is the erosion of the component parts of the ion source due to incidental sputtering of material from the surface of such component parts. This incidental sputtering reduces the operating life of such component parts and also increases the costs of maintenance and of operating the ion source.
Still another problem associated with incidental sputtering of material from surfaces of component parts is that the material sputtered from these surfaces may be deposited onto the substrate surface contaminating the material deposited on the substrate or it may create flaws in the materials deposited on the substrate surface.
The present invention discloses a system that addresses each of the above-mentioned problems associated with the existing methods and apparatus used for deposition of films onto the surfaces of substrates. The invention while alleviating the above-mentioned problems does not reduce the existing range of ion source applications. On the contrary, it expands the cold-cathode ion source application range by allowing for source operation at lower gas pressure and improving operation at all pressures. Surprisingly, this invention makes use of a phenomenon known as xe2x80x9ctarget poisoningxe2x80x9d which prior to the instant invention has been considered a serious problem in the processing of substrates using cold cathode magnetron sputtering. Target poisoning occurs when sputtering metal or semiconductor material from a magnetron target in the presence of a reactive gas, such as oxygen. Under these conditions, the target surface tends to develop and sustain a thin ceramic-like insulating layer of oxide that in most cases is the same material that is being deposited on the substrate. This xe2x80x9ctarget poisoningxe2x80x9d results in a lower removal rate of metal from the target and a correspondingly lower deposition rate on the substrate because the ceramic-like insulator is much harder to sputter than the bulk target material. As such the prior art, teaches that the deposition of such ceramic-like insulator should be avoided in magnetron systems by the use of sputtering methods having high removal rates of material from the target surface thereby insuring that oxide will not accumulate. One example of such a method is taught by M. Alex, C. Van Nutt and S. Gupta in ADC-Reactive Sputtering of Al2O3xe2x80x3 attached hereto and hereby incorporated by reference. Efforts to eliminate xe2x80x9ctarget poisoningxe2x80x9d acted to teach away from the direction the instant invention takes in that by focusing on methods to eliminate poisoned surfaces from magnetron sputtering processes it diverted attention away from the beneficial uses of xe2x80x9cpoisoned materialsxe2x80x9d.
The present invention includes a variety of aspects that relate to the process of film deposition onto substrate material using ion sources. The invention addresses the efficiency, the throughput of the deposition process, the range of ion source operating parameters, and the quality of thin film deposition onto substrates.
Accordingly, a significant object of the invention is to produce a stable and consistent supply of electrons over a wide range of discharge parameters. Attaining this goal can be difficult because, as mentioned above, the secondary electron emissions produced by the cold-cathode processing can be low. This invention focuses on increasing the electron emissive properties of various surfaces within and outside of the ion source thereby providing an enhanced supply of electrons.
Another object of the invention is to increase the output of the ion beam of ion sources that do not utilize hot cathodes. When the output of the ion beam is increased, the deposition rate onto the substrate is increased. This increased rate is particularly desirable for the commercial processing of substrates where increased throughput translates into lower cost of production. Increasing the output of the ion beam, however, requires an additional supply of electrons to intensify the discharge inside the ion source and to negate the additional charges generated. The instant invention increases the supply of electrons that in turn allows the use of increased ion beam output.
Still another object of the invention is to reduce the erosion of the ion beam apparatus elements. The erosion of these apparatus elements not only shortens the operating life of the element itself but may also be deposited as a contaminate on the substrates which are being processed. This invention reduces the sputtering of materials from the apparatus elements helping to alleviate both of these problems.
Yet another broad goal of the invention is to provide surfaces with enhanced electron emissive properties for industrial applications that are inexpensive with respect to the initial investment for the enhanced electron emitting surfaces and also inexpensive with respect to maintenance of such surfaces.
Naturally further objects of the invention are disclosed throughout other areas of the specification.